1. Technical Field
The invention relates to a fiber laser and an optical device using the fiber laser.
2. Description of Related Art
A conventional laser device includes a solid-state laser and a wavelength conversion element in a resonator, converts laser light of the solid-state laser device into a harmonic wave, and outputs a green visible light. The conventional laser device separates P-polarization and S-polarization on the basis of difference in reflectance of P-polarization and S-polarization, and emits a single polarized light. In this method, however, the solid-state laser light cannot be converted efficiently into a green laser light and outputted.
Recently, as a laser light source of high output, a fiber laser having a core of solid-state laser medium is developed. The fiber laser includes a solid-state laser fiber having a core doped with optically active rare earth ions such as Nd, Yb, or Er, and an optically reflective element arranged at a specified spacing along the solid-state laser fiber. When a pump light of specified wavelength is entered in the fiber, rare earth ions are excited, and the solid-state laser fiber becomes a gain medium, and a resonator is made by using the optically reflective element, and a laser is oscillated. The optically reflective element is demanded to have characteristics of transmitting the pump light and reflecting the excitation light excited by the gain medium, and are realized by, for example, a grating fiber capable of forming periodic refractive index changes in the fiber and reflecting a specific wavelength by Bragg reflection.
A method of using this fiber laser as a light source of single polarization is disclosed in JP A-11-501158. The polarization control fiber laser in JP A-11-501158 has the laser medium as polarization preserving fiber, and the laser medium is dependent on polarization. The polarization control fiber laser increases the loss on one polarized light, and propagates other polarized light of smaller loss, and thereby outputs a single polarized light. Further, the ray of fiber laser is coupled to an optical fiber amplifier, and a ray of high intensity is released from the optical fiber amplifier. Thus, the conventional fiber laser oscillates the laser in a mode of smaller loss in the resonator based on the polarization control of increasing the loss of one polarized light of two different polarized light components.